It is conventionally known to prepare photosensitive copying materials from diazo resins, or condensates of formaldehyde and p-diazodiphenylamine. The production of these polyfunctional diazo resins is described in U.S. Pat. Nos. 2,679,498, 3,050,502, 3,311,605, 3,163,633, 3,406,159 and 3,277,074. In order to improve the long-term stability of water-soluble diazo resins, they may be rendered water-insoluble and olephilic by reacting them with coupling agents such as acidic aromatic compounds. Methods to achieve this object are described in Japanese Patent Publication No. 1167/72 and U.S. Pat. No. 3,300,309.
However, these conventional diazo resins do not have high solubility in organic solvents such as glycol ethers, alcohols and ketones even if the counter-ion to be paired with the diazonium group is an inorganic ion derived from a hydrohalogenic acid or phosphoric acid or an organic ion derived from an acidic aromatic compound such as benzenesulfonic acid or toluenesulfonic acid.
The sensitivity of these diazo resins may be improved by increasing their molecular weight (degree of polymerization). However, molecular weight control is not easy in condensation reactions from a synthesis point of view. What is more, resins with an increased molecular weight have a significantly reduced solubility in organic solvents and may experience decreased resolution.
Furthermore, the condensate of p-diazodiphenylamine and formaldehyde is very difficult to handle under incandescent lamps without causing fog because it decomposes by absorbing light in the visible spectrum of 420 to 500 nm. This presents a serious problem from a manufacture and use point of view.
Diazo compounds having a polyester group in the backbone are described in Japanese Patent Application (OPI) No. 30121/79 (the symbol OPI as used herein means an unexamined published Japanese patent application), but they are produced by a very special method which is not applicable to other cases. In addition, the ester group in the backbone cleaves so easily that the sensitivity of the diazo compound is decreased during storage after its preparation or application to a photographic support, and as a result, the commercial value of the final product is greatly impaired.
The present inventors have made detailed and extensive studies to eliminate these defects of the known diazo resins, and as a result, they have found a novel diazonium salt containing high-polymeric compounds characterized by high sensitivity and protection against fog under incandescent lamps.